Process for surfacing electrodes for electrical-discharge tubes



Patented Sept. 24', 1935 PATENT OFFICE-I PROCESS FOR SURFACING ELECTRODES 'FOR. ELECTRICAL-DISCHARGE TUBE-S Albert C. Forst, Alameda, Calif.

- No Drawing.

Application July 26, 1932,

Serial'No. 624,909

2 Claims. (0]. 176-126) The invention relates to processes employed in cleansing and coating the metal surfaces of electrodes, such as employed in electrical-discharge tubes, for the purpose of rendering these surfaces more eflicient in their operation on the electrode.

The essential purpose of treating and coating electrode surfaces by processes of the class here disclosed is to render these surfaces of such a nature that they may cooperate most effectively with the shape of the electrode to support about the latter an-electrostatic field that will cause a confinement of the electrical discharge to a relatively small portion of the surface and at the same time prevent-corona and other undesirable discharge from occurring over the remainder' of the surface. Such a surface treatment usually comprises covering the entire electrode, other than a relatively small portion,

with an insulation coating and rendering the uncoated portion of a nature to withstand sustained electronic bombardment without materially affecting its conductivity. Processes for carrying out such a'surface treatment have beenv used on electrodes 'of certain metals, especially copper and iron, but to my knowledge none of these processes has'been successful when applied to a metal such as aluminum. This latter metal has manyinherent qualitiesof advantage over both copperand iron, particularly in its'availability in a substantially pure form that is remarkably free from impurities and excessive quantities of entrapped surface gases which when released in a gaseous electrical discharge tube harmfully disturb the character of the light emitted. It theref e forms one of the principal objects of my invention to provide a. process of the character aforesaid which may be 'espe cially and efiicaciously applied to electrodes of aluminum. 1

Another object of the invention is to provide a process of the character described which will substantially completely liberate gases'entrapped in the surfaces of the electrode and thereafter seal the surfaces. against reabsorption of such gases.

A further object. of the invention is to provide a process for treating and coating the surfaces 'of electrodes which will materially increase the ability of such surfaces to withstand intense heat as well as heavy electronic bombardment tionof the preferred form of the invention. It

is to be understood, however, that variations in the showing made by the said description may be adopted within the scope of the invention as set forth in the claims.

In accordance with the process of my invention, it is desirable to first effect .a thorough cleaning of the electrode surfaces to be coated, and for this purpose the electrode is boiled in water from ten to thirty minutes to remove the 10 soluble surface impurities and to cause any oil or grease present on the velectrode to be dislodge and separated therefrom, the free oil and g ase naturally rising to the surface of the water om where it may be removed. After 15 being initially cleaned in this manner, the electrode is removed from the water withoutcontact with the oil 05 greaseand placed in a bath of oxalic acid, diluted with about four parts water, and left in the acid from four to twelve hours. 20

The action of the acid on the aluminum is to form a film of aluminum oxide over the surface the acid bath is rinsed in cold water, "dried and then heat treated to causeea fusion of the oxide. on the surface of the metal. ment may be'eflected either by contacting the electrode directly with a clean flame or placing the same in a suitable oven and gradually rais- .ing the temperature of the electrode 'to a dull red heat, after which the electrode is removed 35 from the presence of the heat and allowed to cool. A

The fused oxide surface serves a dual purpose" for it -not only forms an excellent conducting surface for the discharge emitting portion of the 40 problems in the useof electrodes of this metal. 45

In accordance with my process,- however, having provided a fused oxide base upon which to build, I proceed by coating this base. with the exception of the area providing the discharge portion of the electrode, with a vitreous enamel and again subject thev electrode to a relatively high heat in order to fuse the enamel into a glaze thereby forming an insulation covering over the surface I of the electrode. Any suitable low fusing vitreous' glaze using finely ground glass, porcelain or lava The heat treat tube as a base may be used. The heat treatment of the surface for fusing the glaze may in the first instance be carried out either over a flame or in an oven, and the temperature 'of thesurface is preferably raised to a dull red heat and there The final heat treatmentafter allowed to cool. in addition to fusing the enamel serves to liberate surface gases on the electrode and fuse the enamel into surface sealing relation which checks reabsorption of the gases upon cooling of the surface.

With the surfaces of the electrode thus freed from and sealed against absorption of surface gases and impurities, the probable quantity of inert gases and foreignmaterial other than the rarlfled gas in an electrical discharge tube may be accurately determined and depended upon to remain constant over long periods of use. l 'ormerly it was necessary during the filling of the tube with the rarifled gas to not only include.

sumcient of the latter to subdue the effects of the foreign gese and impurities present at the outset, but in addition supply an over-abundance of such rarifled gas to overcome the effects of foreign gases and other impurities which are subsequently liberated by the electrodes after the been in operation for some time. This latter quantity of gas which is added with the expectancy of satisfying subsequent gaseous conditions in the tube has in the past been a source of much waste and uncertainty. In accordance with the process of my invention, however, it will a be apparent that the-electrodes are so surfaced and treated as to substantially entirely prevent the subsequent liberation of foreign gases or impurities, and therefore enable the use of a minimum and absolutely consistent quantity of rari- 10 fled gasf thereby effectively serving to eliminate the aforesaid waste and uncertainty.

It will now be clear that the process of my invention is well adapted to the accomplishment of the objects hereinbefore referred to. 15

I claim:

1. A process for surfacing aluminum electrodes for gaseous electrical discharge tubes which comprises treating said electrode with oxalic acid, thereafter heating sald electrode to dull red at 20 and cooling, and thereafter fusing onto said electrode a vitreous coating.

2. An electrode for gaseous electrical discharge tubes of neon and the like comprising, an aluminum member having a base surface coating of 25 a fused layer-of aluminum oxide, and an outer layer of a fused vitreous substance.

ALBER'IB C. EORST. 

